Hemoglobin is an intracellular protein whose main function is to transport oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. The hemoglobin molecule is made up of four polypeptide chains, two identical. Three types of hemoglobin circulate in the blood of a healthy adult:
- Hemoglobin A1: 97% of total hemoglobin composed of 2 alpha and 2 beta chains
- Hemoglobin A2: 2.2- 3.1% of total hemoglobin, composed of 2 alpha and 2 delta chains
- Hemoglobin F: < 1%, composed of 2 alpha and 2 gamma chains.
Thalassemias are a heterogeneous group of hereditary anemias that occur as a result of insufficient synthesis or the absence of one or more globin polypeptide chains in the hemoglobin molecule. The defect can affect any of the four polypeptide chains of normal hemoglobin – alpha, beta, delta or gamma, and this determines the type of thalassemia syndrome.
Alpha and beta thalassemias are the most common, and beta thalassemia is the most common in Bulgaria. In this disease, the synthesis of beta polypeptide chain is reduced to varying degrees. The degree to which synthesis is reduced distinguishes severe from mild anemia.
Thalassemia minor is the milder form of the disease, which is characterized by one normal and one defective gene. The normal gene dominates and for this reason the disease is often asymptomatic and may remain undiagnosed. This type is characterized by a reduced level of hemoglobin A1, increased hemoglobin A2 and, in some cases, an increase in hemoglobin F.
Thalassemia major (Culei’s thalassemia) is the more severe homozygous form of the disease and is characterized by the presence of 2 pathological genes. In this condition, the level of hemoglobin A1 is very low and the level of hemoglobin F is greatly increased, which can reach up to 90% of total hemoglobin. Clinically, anemia manifests itself after 6 months of age, and some of the symptoms include severe anemia, jaundice, enlargement of the spleen, skull deformity, and significant retardation in growth and development. Critically low hemoglobin requires specific treatment.